Demand for a nonvolatile storage module including a rewritable nonvolatile memory, mainly semiconductor memory cards, is increasing as a detachable storage device. Although the semiconductor memory card is much more expensive than an optical disc, a tape media and the like, due to merits such as compact size, light weight, resistance to seismic shocks and convenience in handling, its demand as a recording medium for portable equipment such as digital still cameras and mobile phones has been expanded.
The semiconductor memory card includes a flash memory as a nonvolatile main memory, and has a data reader that controls the flash memory. The data reader controls reading/writing with respect to the flash memory according to a reading/writing instruction from the access module such as the digital still camera. There are also nondetachable nonvolatile storage modules that are incorporated into the digital still camera or portable audio equipment main unit, or incorporated into a personal computer in place of a hard disc.
The flash memory includes a memory cell array and I/O register (RAM) that temporarily holds data read from the memory cell array or temporarily holds externally written data. Since the flash memory requires a relatively long time to write data to or erase data from memory cells forming the memory cell array, the flash memory is structured to be capable of writing data to or erasing data from a plurality of memory cells all together. Specifically, the flash memory is configured of a plurality of physical blocks and the physical blocks each have a plurality of pages. Data erasure is performed in physical block units and data writing is performed page units.
There exists a musical sound generation system which holds musical sound data of an electronic musical instrument or the like in a ROM. The musical sound generation system is a system that generates sound of the musical instrument (hereinafter referred to as musical sound) in response to a keystroke operation such as stroking a key. The musical sound generation system generally has 32 channels or more of sound production channels and for example, assigns the sound production channel in the order of keystrokes to generate the musical sound. Since the musical sound needs to be generated in response to a random key striking operation in this system, a mask ROM having a high random reading rate is used as the ROM for the musical sound data.
According to Patent document 1, with technical progress of the flash memory, it is estimated that a bit unit cost of the flash memory becomes lower than a bit unit cost of the mask ROM. The document discloses a technique of reducing system costs by using the flash memory having a lower random reading rate than the mask ROM as the ROM for musical sound data.
As estimated, to address a demand for larger capacity and lower costs, a gigabit class of multi-level NAND flash memory has become dominant by value multiplexing and process shrinking. As a result, the flash memory has a much more inexpensive bit unit cost and much larger capacity per unit area than the mask ROM and therefore, the possibility of a lower price and smaller size of the system has been increased more and more.
A binary NAND flash memory (product number: TC58V64FT) used in an embodiment of Patent document 1 is an old-type of small-capacity and high-speed flash memory in binary NAND flash memories, in which a capacity is 64 Mbits and a read time (hereinafter referred to as TR) required to access from the memory cell array to the I/O register and read data is 7 μs.
[Patent document 1] Japanese Unexamined Patent Publication No. 2000-284783